Method and apparatus for transmitting ultrasound pulses and receiving echo signals at a harmonic of the transmission frequency

ABSTRACT

A method for transmitting ultrasound pulses and receiving echo signals at a harmonic of the transmission frequency includes the steps of generating a signal for exciting a transducer to transmit at least one ultrasound pulse at a basic transmission frequency and receiving the reflection echo of said pulse at a harmonic of the frequency of the transmitted pulse, any contributions to the harmonic frequency being removed or attenuated in the signal for exciting pulse transmission, characterized in that the signal for exciting the transducer/s is filtered or coupled thereto via a resonant circuit which is calibrated to the basic frequency. In combination therewith or alternatively thereto, the method includes a resonant circuit for additional coupling with a receiver. Included is an apparatus for transmitting ultrasound pulses and receiving echo signals at a harmonic of the transmission frequency, particularly an ultrasound imaging probe and an ultrasound imaging machine.

REFERENCE TO RELATED APPLICATION

[0001] The present patent application claims foreign priority benefitsunder 35 U.S.C. §119 to Italian patent application No. SV2001A000030,filed Aug. 14, 2001, now pending.

BACKGROUND OF THE INVENTION

[0002] The present invention relates generally to a method fortransmitting ultrasound pulses and receiving echo signals at a harmonicof the transmission frequency including the steps of generating a signalfor exciting a transducer to transmit at least one ultrasound pulse at abasic transmission frequency and the steps of receiving the reflectionecho of said pulse at a harmonic of the frequency of the transmittedpulse, any contributions to the harmonic frequency being removed orattenuated in the signal for exciting pulse transmission. Included aspart of the present invention is an apparatus for practicing thedescribed method.

[0003] In ultrasound imaging machines operating in the harmonic imagingmode, signal generators are provided for exciting an array oftransducers to transmit ultrasonic pulses at a certain frequency. Theultrasonic pulses transmitted at a certain basic frequency toward a bodyunder examination are backscattered and the transducers are used assensors for receiving the reflected echo signals at a harmonic of thebasic frequency of the transmitted pulses, typically at the secondharmonic frequency, the electric signals generated by said transducersbeing provided to a receiver.

[0004] This ultrasound imaging mode is very useful when contrast agentsare used for valid diagnostic imaging of spontaneous flows of bodyfluids, such as blood flows or the like, which are poorly echogenic.Unlike substantially stationary tissues, which have an echogenicbehavior, contrast agents have a nonlinear reflection behavior, hencethe backscattered echo signals have harmonic frequencies, especiallycorresponding to the second harmonic of the basic frequency of thetransmitted pulses. Therefore, the reflection contributions provided byfluid flows in which contrast agents are injected may be distinctlyseparated, with no risk for the latter to be dazzled by the reflectionsignals of stationary tissues, which have definitely higher intensities.

[0005] Nevertheless, transmitted pulses are currently not completelypure, but include harmonic components. This is partly due to thespecific characteristics of the generator-transducer assembly, andpartly to the fact that, even when pure sinusoidal waves are provided,pulse formation, i.e. the time cut of the waveform or time limitthereof, necessarily causes the generation of such spectra as to includeharmonic frequencies. The presence of components whose frequenciescorrespond to at least one harmonic, and particularly to the secondharmonic of the basic frequency in the transmitted pulses causes theecho signals to be distorted by said components. Therefore, there is theneed to remove or drastically attenuate all components having harmonicfrequencies in the transmitted signals.

[0006] It is known from U.S. Pat. No. 5,833,614 (issued Nov. 10, 1998 toDodd et al.) to superpose the transmission signal provided by thegenerator to the transducer with an additional signal or pulse forattenuating or removing the harmonic components, for instance a pulsewith the same profile as a Gaussian curve having the maximum at thebasic frequency. This signal must be specially generated and superposedin a synchronized manner.

[0007] Nevertheless, this is a highly complex system which requireslinear pulsers, therefore it is expensive and has a low electricalperformance, which makes it incompatible with small and/or low-costapparatuses.

[0008] Therefore, the present invention has the object of providing amethod and an apparatus as described hereinbefore which, by simple andinexpensive arrangements, allow to remove any harmonic components in thetransmitted pulses without using linear pulsers and to remove spuriousharmonic components introduced upon reception of echo signals in amanner that is substantially independent from the type of probe in useand anyway not requiring complex and difficult adaptation methods.

[0009] The present invention achieves the above purposes by providing amethod as described herein, in which the signal for exciting thetransducer/s is filtered or coupled thereto through a resonant circuitcalibrated to the basic frequency.

[0010] Particularly, a resonant circuit for coupling to the generator isgenerated, which upon transmission, resounds at the basic frequency ofthe transmitted pulses.

[0011] Alternatively thereto or in combination therewith the presentinvention provides that the transducer/s are filtered or coupled to thereceiver through a resonant circuit which is calibrated to the receiveharmonic frequency, particularly to the second harmonic of the basicfrequency of the transmitted pulse.

[0012] A resonant circuit is actually provided which, upon reception,resounds at the predetermined harmonic frequency, particularly at thesecond harmonic frequency.

[0013] According to an improvement, the method of the present inventionprovides the use, as a transmitting resonant circuit, of the assemblycomposed of the transducer/s and the cable connecting it to atransmitter which generates electric pulses for exciting thetransducer/s, the resonance frequency being adjusted to the basicfrequency by inserting an inductance in series between the connectingcable and the transmitter.

[0014] Since the inductance value for determining the resonancefrequency is determined by specific electric characteristics of theprobe assembly, composed of the transducers and the connecting cable,the inductance may be appropriately selected for each type of probe andbe mounted in advance on the cable or the probe itself.

[0015] The above is based on the acknowledgement that the cable-probeassembly actually is a resonant circuit having measurable capacitanceand resistance values. Therefore, for each probe-cable combination, itis possible to determine the inductance value required to calibrate theresonant circuit to the basic frequency. The behavior of the resonantcircuit is independent from the generator or transmitter, as thetransmitter actually is a low-impedance generator.

[0016] According to a further improvement, regarding the receivingresonant circuit, the latter consists of the receiver itself which, uponreception, operates like a resonant circuit having predeterminedresistance and capacitance values, whereas the cable-transducer ortransducers/cable assembly behaves like a low to medium impedancegenerator.

[0017] As provided for transmission tuning, a tuning inductance is alsoprovided upon reception.

[0018] Here, the analysis of typical resistance and parasiticcapacitance values of receivers surprisingly showed that the same tuninginductance used to calibrate the transmitting resonant circuit may beused for the receiving resonant circuit.

[0019] In fact, the parasitic capacitance was generally found to besufficient to cause the receiving resonant circuit to be properly tunedto the second harmonic frequency in combination with the inductance fortuning the transmitting resonant circuit.

[0020] However, if the parasitic capacitance of the receiver combinedwith the tuning inductance value provided for the transmit circuit isnot suitable for tuning the receiving resonant circuit to the frequencyof the selected harmonic, particularly of the second harmonic, acompensating capacitor may be provided, parallel to the parasiticcapacitance of the receiver.

[0021] In this case, the sum of the parasitic capacitance of thereceiver and of the compensating capacitance is selected as a quarter ofthe total capacitance of the probe-cable, or transducer/s-cableassembly, and the compensating capacitor does not affect the behavior ofthe transmitting resonant circuit.

[0022] Regarding the need to have a resonant circuit in the receivingchain, it shall be noted that, although the provision of this resonantcircuit is certainly desirable, the latter is not so critical as for thetransmitting resonant circuit. In fact, the transmitted pulses arealready intrinsically free or substantially free of harmonic components,hence the generation of artifacts due to said components of thetransmitted pulses is already widely suppressed or attenuated.Nevertheless, the presence of a resonant circuit properly tuned to thesecond harmonic is advantageous both to further limit the harmoniccomponents due to parasitic processes and to cause, already uponreception, the basic band reflection signal to be filtered, withoutusing or substantially limiting the procedures to extract, uponreception, the second harmonic signal from the reflected signals whichobviously contain relatively high power or intensity components at thebasic frequency. Although, when a compensating capacitor is provided,the latter is to be optimized based on the capacitance of thetransducer/s-cable assembly and on the parasitic capacitance of thereceiver, it should be understood that the generators typically havesubstantially similar constructions and in most cases, the parasiticcapacitances are substantially identical and of the same order ofmagnitude. Anyway, even when the latter were not true, compensatingcapacitor are relatively easily adaptable, by using a variablecapacitor, e.g. manually controlled for tuning and/or automatically setby the machine thanks to an automatic procedure for determining electricvalues through direct measurement by the ultrasound imaging machine orby plug-and-play protocols, whereby the relevant data of the probe ortransducer or transducers-cable assembly and/or the data of the receiverare stored in a special portion of the memory associated to one of thecomponents of the probe-cable assembly and/or of the receiver.

[0023] This mode also provides the opportunity to obtain an automatictuning system which, by reading the technical electric characteristicsof the probe-cable assembly and/or of the receiver, controls either avariable inductance or a variable compensating capacitor to achieve theoptimized tuning conditions as better specified above.

[0024] Alternatively to the above, the type of probe-cable assembly maybe also recognized with the help of tables stored in the apparatus,which provide information on said assembly associated to a probeidentification code. In this case, the probe may be selected manually,based on the name or identification code thereof, or the assembly hasthe identification code stored therein so that, upon connection, theapparatus reads the identification code provided by the probe, finds thecorresponding table of characteristics and sets the inductance andpossibly the compensating capacitor based on the characteristics definedin the table.

[0025] A system might be also provided, whose operation is identical toloading of drivers for computer peripheral devices. In this case, areadable storage medium is provided with the probe, such as a floppydisk, a CD-Rom, a batchcard or the like, the apparatus including areader of the storage medium. A special system including a dedicatedmicroprocessor or the processing unit itself of the ultrasound imagingmachine and at least one memory or memory area dedicated to the storageof tables of characteristics, transfers data from the reader to saidmemory or memory area by using it according to a set-up program forautomatically setting inductance and possibly compensating capacitor tothe proper values for the probe-cable assembly. The procedure issubstantially the same as is used to load peripheral drivers incomputers.

[0026] Obviously, besides the above, other automatic or semiautomaticmodes may be provided to recognize the probe-cable assembly and to settuning inductances and compensating capacitors.

[0027] In accordance with a further improvement, the present inventionprovides the combination of a frequency filtering process upontransmission and/or reception of ultrasonic transmitted pulses andreflection echoes respectively, by using a multiple pulse imagingtechnique, which provides that image data is obtained by combining thereflected echoes of at least two successive identical transmitted pulsesfocused along the same line of view. These combinations may be adifference between the reflection echoes provided by two identicaltransmitted pulses or a sum of two successive transmitted pulses, whichare inverted, i.e. 180° dephased, like in the Pulse Inversion technique.

[0028] The above mentioned combination arranges the transducer/s, or theprobe to be coupled, through a resonant circuit, to the transmitterand/or the receiver, and at least two successive identical or invertedtransmitted pulses, in which reflection echoes are subtracted or addedrespectively, image data being obtained from said difference or sumsignal.

[0029] The combined use of the method of the invention with the abovemultiple pulse modes generates a synergistic effect which allows toobviate the drawbacks of multiple pulse modes and to improve the methodof this invention.

[0030] In fact, the coupling through resonant circuits appropriatelycalibrated for transmission and reception has the advantage of providinga frequency filtering action on the reflection echoes, aimed atextracting the harmonic component and particularly the second harmoniccomponent of echoes, thus being a very simple method of extracting thereflection signals caused, for instance, by contrast agents.Nevertheless, frequency filtering requires a distinct separation betweentransmission and reception which are to be performed with a relativelynarrow frequency band. This may cause a low axial resolution, hence apoor discrimination of reflection echoes, caused by neighboring pointson the same axis of the line of view On the other hand, while themultiple pulse techniques meet the requirement of very narrow transmitand receive bands, they have the drawback of being affected by motionclutters on received signals.

[0031] By combining the two techniques, relatively wider transmit and/orreceive passbands may be provided, thanks to multiple pulse techniques,such as Pulse Inversion or the like, thereby obtaining a betterresolution and at the same time removing motion clutters thanks to aproper tuning of the resonant circuits which allow coupling with thetransducer/s or the probe to the transmitter and/or the receiver.

[0032] Also, according to an improvement, since multiple pulsetechniques, e.g. the Pulse Inversion technique, allow to remove thereflection signals associated to spurious components, particularly toharmonic components in transmitted pulses, it is sufficient to onlyconnect the receiver through a resonant circuit calibrated to thedesired receive frequency, e.g. to the second harmonic frequency.

[0033] An ultrasound multiple pulse imaging technique is described in EP0770352 which was published May 2, 1997.

[0034] These multiple pulse techniques may also consist of techniquesemploying modulated wavelets which provide coding upon transmission andcorrelated filtering upon reception, wherein the term wavelets includesarbitrary analog signals not having discrete times and amplitudes aswell as pulse sequences having discrete times and amplitudes, such asthe technique described in U.S. Pat. No. 6,050,947 (issued Apr. 18, 2000to Rhyne et al.) whose disclosure is expressly incorporated by referenceherein.

[0035] Alternatively, multiple pulse techniques may also include a PulseInversion technique, in which only a few components of the at least twosuccessive transmitted pulses are inverted, whereas the other componentsare not inverted, the reflected signals of the two successive pulsesbeing summed upon reception. A technique of this type is described inU.S. Pat. No. 5,902,243 whose content is integrated herein by reference.

[0036] The invention also relates to an apparatus for transmittingultrasound pulses and receiving echo signals at a harmonic of thetransmission frequency, for example to an ultrasound imaging machinecomprising:

[0037] a transmitter which generates electric signals for exciting atleast one transducer to transmit ultrasound pulses at a predeterminedbasic frequency, a receiver whereto electric signals are provided fromone or more transducers which pick up reflected echo signals at aharmonic frequency, particularly a second harmonic of the frequency ofthe transmitted pulses and means for removing or drastically attenuatingthe contributions of harmonic components, particularly those at thesecond harmonic in transmitted pulses, said means consisting of aresonant circuit which allows to couple the transducer/s to thetransmitter, whose resonance frequency is set to the basic frequency ofthe transmitted pulses.

[0038] Particularly, the resonant circuit consists of the assemblycomposed of the probe, i.e. the transducer/s thereof and the connectingcable, there being provided an inductance for tuning the resonancefrequency of said resonant circuit to the basic frequency of thetransmitted pulses.

[0039] Particularly, the tuning inductance is connected in series to theresistor of the assembly composed of the probe or transducer/s thereofand the output of the transmitter.

[0040] The transmitter is a low-impedance generator In accordance withan additional characteristic, which may be provided as an alternativethereto or in combination therewith, the apparatus includes a resonantcircuit for coupling the receiver to the assembly composed of the probeor transducer/s thereof and the connecting cable, which is tuned to aresonance frequency corresponding to a predetermined harmonic,particularly to the second harmonic of the basic frequency of thetransmitted pulses.

[0041] Advantageously, the resonant circuit consists of the receiver,i.e. of the resistor and the parasitic capacitance thereof.

[0042] When the parasitic capacitance of the receiver, besides providingthe inductance for tuning the transmitting resonant circuit does notallow to tune the receiving resonant circuit to said harmonic frequency,a compensating capacitor may be provided.

[0043] The compensating capacitor is connected in parallel to theparasitic capacitance of the receiver.

[0044] Particularly, it is advantageous to provide such a compensatingcapacitor that the sum of the parasitic capacitance of the receiver andthe compensating capacitance substantially corresponds to a quarter ofthe capacitance of the transmitting resonant circuit, i.e. of theassembly composed of the probe or the transducer/s thereof and theconnecting cable.

[0045] The advantages of the present invention are self-evident from theabove description. The specific inductance for tuning the transmittingresonant circuit may be mounted on the probe-cable assembly. Hence, eachprobe is adapted regardless of the apparatus, i.e. of the transmitterthereof whereto it will be coupled. The operation is performed on theprobe and does not need to account for the transmitter and thecharacteristics thereof. As a transmitter, a sinusoidal transmitter maybe used, which is highly cost-effective.

[0046] Typically, the receiving resonant circuit is tuned in asubstantially automatic manner, and the specific compensating capacitorof the receiving resonant circuit may be anyway provided thereon. Thevalue of such capacitance may be adjusted by a special control, e.g.thanks to a variable capacitor, in a simple and fast manner. Moreover,it shall be noted that, upon reception, tuning is less critical asregards reception of spurious signals, because, with high-qualitytransmitted pulses, as regards removal or attenuation of harmonicfrequencies, the reflected signals at harmonic frequencies will alreadyhave a lower probability of containing harmonic components not due tocontrast agents but generated by parasitic effects.

[0047] With reference to a further improvement, the apparatus of theinvention includes at least one transmitter and at least one transducerhaving a cable for connecting it to the transmitter and a memory, acontrol unit and a variable and adjustable inductance, which may becontrolled by the control unit, the electric characteristics of thetransducer-connecting cable assembly being loaded in the memory togetherwith a software program for reading said electric characteristics andfor controlling the inductance to tune the resonant circuit formed bythe transducer-connecting cable assembly to the basic frequency of thetransmitted pulse, which program is automatically executed uponconnection of the transducer-cable assembly to the transmitter bysensors for detecting the electric conditions of the connectinginterface between the transducer-cable assembly and the transmitter.

[0048] The memory may be steadily mounted in the transducer-cableassembly.

[0049] A variant embodiment provides two memories, a first memory beingmounted on the transducer-cable assembly, wherein an identification codefor said assembly is stored, and a second memory being associated to thetransmitter and to the control unit, for storage of all data relating tothe electric characteristics of several different transducer-cableassemblies, which are uniquely identified by an identification code, theidentification code of each transducer-cable assembly being read uponconnection of said assembly, by the control unit, and the data relatingto said identification code being searched in the second memory toexecute, based on said data, the program for setting the variableinductance to tune the transmitting oscillating resonant circuit.

[0050] An additional improvement provides the further combination of anexternal portable storage medium for storing the electric data of apredetermined transducer-cable assembly and a reader of said mediumconnected to the control unit, there being provided a program forcausing said data to be loaded from the portable storage medium into thesecond memory when in said second memory no data identified by theidentification code of the transducer-cable assembly is present.

[0051] In accordance with yet another improvement, the apparatus alsoincludes a receiver and an alternative circuit for connecting thetransducer-cable assembly to the transmitter and to the receiver, therebeing provided an variable capacitor for compensating the parasiticcapacitance of the receiver to tune the receiving resonant circuit, andthere being provided a software program for controlling the variablecapacitor to the proper value to tune the receiving resonant circuitbased on the data of the electric characteristics of thetransducer-cable assembly connected to the receiver, which is executedby the control unit, in the same manner as the transmit resonant circuitis tuned.

[0052] The transducer-cable assembly includes several transducers and isparticularly composed of an ultrasound imaging probe and thecorresponding connecting cable.

[0053] The transmitting and/or receiving apparatus consists of thecorresponding unit of an ultrasound imaging machine.

[0054] The second memories and the control unit, as well as possibly thereader of the portable storage media are memories, processors andstorage media readers which are already included in the ultrasoundimaging machine.

[0055] Therefore, the invention also relates to an ultrasound imagingprobe comprising at least one transducer for turning electric signalsinto ultrasound transmit pulses, e.g. a piezoelectric transducer and acable for connecting said probe to an ultrasound imaging apparatus,there being provided an inductance for tuning the resonant circuitformed by the capacitor and the resistor of the probe-cable assembly.

[0056] The inductance may be adjustable and controllable by a centralunit outside the probe and included, for instance in an ultrasoundimaging machine.

[0057] Further, the probe and/or the cable for connecting it may includea memory which contains the data relating to at least one uniqueidentification code for said probe-connecting cable assembly and/or thedata of the capacitance and resistance values of the equivalent resonantcircuit formed by said probe-connecting cable assembly, the memory beingreadable through the connecting cable by a processing and control unitof an ultrasound imaging machine.

[0058] The invention also relates to an ultrasound imaging apparatusincluding at least one transmitter with a connection interface and atleast one ultrasound imaging probe-connecting cable assembly, saidinterface having an inductance for tuning the resonant circuit formed bysaid probe-connecting cable assembly.

[0059] Also, the ultrasound imaging apparatus includes a processing unitfor reading a memory containing all data relating to the electricresistance and capacitance characteristics of the probe-connecting cableassembly, for a predetermined type of such an assembly, to be uniquelydefined by an identification code, which sets the value of a variableinductance for tuning said resonant circuit based on said data.

[0060] The ultrasound imaging machine also includes a receiver and meansfor alternatively connecting the probe-connecting cable assembly to thetransmitter and to the receiver.

[0061] In accordance with an improvement, said ultrasound imagingapparatus includes a capacitor for compensating the parasiticcapacitance of the receiver which, upon reception, forms a resonantcircuit, to tune said resonant circuit to a predetermined frequency.

[0062] Advantageously, said compensating capacitor is variable and isset on the value which allows tuning to the frequency selected, inaccordance with the data of the electric characteristics of theprobe-cable assembly, by the processing and control unit of the machine.

[0063] The present invention further relates to an apparatus fortransmitting ultrasound pulses and receiving echo signals as describedherein, for instance an ultrasound imaging machine including atransmitter which generates electric signals for exciting at least onetransducer to transmit ultrasound pulses at a predetermined basicfrequency, a receiver whereto electric signals are provided from one ormore transducers which pick up reflected echo signals at a harmonic orsub-harmonic frequency, particularly a second harmonic of the frequencyof the transmitted pulses and a resonant circuit through which thetransducer/s are coupled to the receiver, whose resonance frequency isset to a harmonic or sub-harmonic frequency of the basic frequency ofthe transmitted pulses, particularly to a second harmonic of thefrequency of the transmitted pulses, there being provided means fortransmitting, for each line of view, at least two successive identicalor phase-inverted transmission pulses and means for combining thereceived reflection echoes, caused by said two pulses in the form of asubtraction or a sum of the two reflection echoes respectively, such asa summer or subtracting circuit.

[0064] In combination with the above, a device may be provided in whichthe transducer/s, i.e. the probe, is also coupled to the transmitterthrough a resonant circuit calibrated to the fundamental frequency ofthe transmitted pulses.

[0065] Said transmitting and/or receiving resonant circuits may beprovided as described above and in any of the above combinations andsub-combinations.

SUMMARY OF THE INVENTION

[0066] A method for transmitting ultrasound pulses and receiving echosignals at a harmonic of the transmission frequency according to oneembodiment of the present invention includes the steps of generating asignal for exciting a transducer to transmit at least one ultrasoundpulse at a basic transmission frequency, receiving the reflection echoof the pulse at a harmonic of the frequency of the transmitted pulsewherein any contributions to the harmonic frequency are removed orattenuated in the signal for exciting pulse transmission, the inventionbeing characterized in that the signal for exciting the transducer isfiltered or coupled thereto by way of a resonant circuit which iscalibrated to the basic frequency. A related embodiment of the presentinvention comprises an apparatus for practicing the method.

[0067] One object of the present invention is to provide an improvedmethod and apparatus for transmitting ultrasound pulses and receivingecho signals at a harmonic of the transmission frequency.

[0068] Related objects and advantages of the present invention will beapparent from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0069]FIG. 1 shows a block diagram of an ultrasound imaging machineaccording to a typical embodiment of the present invention.

[0070]FIG. 2 shows the equivalent diagrams of a transducer-cableassembly and transmitter associated with the FIG. 1 ultrasound imagingmachine.

[0071]FIG. 3 shows the equivalent diagrams of a transducer-cableassembly and receiver associated with the FIG. 1 ultrasound imagingmachine.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0072] For the purposes of promoting an understanding of the principlesof the invention, reference will now be made to the embodimentsillustrated in the drawings and specific language will be used todescribe the same. It will nevertheless be understood that no limitationof the scope of the invention is thereby intended, such alterations andfurther modifications in the illustrated device, and such furtherapplications of the principles of the invention as illustrated thereinbeing contemplated as would normally occur to one skilled in the art towhich the invention relates.

[0073] Referring to FIG. 1, an ultrasound imaging apparatus includes acentral unit 1 which controls a transmission channel 2 having atransmitter 3. Moreover, the central unit 1 also controls a receivingchannel 4 having a receiver 5. The transmitter 3 and the receiver 5 areconnected to a probe 6 by means of a switching and ultrasonicbeam-forming unit 7.

[0074] Memories 8, a display screen 9 and a unit 10 for reading/writingportable storage media are further connected to the central processorunit 1.

[0075] The probe 6 includes a plurality of transducers 106 which areconnected together by the cable 206. The cable 206 is also connected tothe switch 7, hence to the transmitter and the receiver by means of aninductance 12, whereas the probe and the cable are connected to thereceiver 5 by means of both the inductance 12 and a capacitor 13 whichis inserted in the circuit in parallel with the parasitic capacitance ofthe receiver 5.

[0076]FIGS. 2 and 3 show an equivalent circuit upon transmission andreception respectively, i.e. when the switch 7 connects the probe 6 andthe cable 206 to the transmitter 3 and the receiver 5 respectively.While the transmission and receiving channels are physically joined by aseparator circuit, i.e. the switching unit 7, the equivalent circuitsthereof are different. Particularly, upon transmission, the transmitter3 operates like a low impedance generator, whereas the assembly composedof the probe 6 and the cable 206 actually forms a resonant circuit.Conversely, upon reception, the receiver 5 operates like a resonantcircuit, whereas the probe-cable assembly operates like a low to mediumimpedance generator.

[0077] Therefore, due to the above, in order to remove or drasticallyattenuate the harmonic components, particularly those having a secondharmonic frequency in the transmitted ultrasonic pulse and to remove ordrastically attenuate the contributions to the received signal havingfrequencies other than those at a predetermined harmonic of thefundamental transmission frequency, e.g. at the second harmonic, thefollowing tuning condition may be used for oscillating resonantcircuits.

[0078] By inserting an inductance 12 having an appropriate value betweenthe assembly composed of the probe 6 and the cable 206 and thetransmitter 3 and the receiver 5, the corresponding oscillating circuitmay be calibrated, i.e. the circuit formed by said probe-cable assemblymay be calibrated to the resonance frequency corresponding to thefundamental frequency of transmission pulses, and the circuit formed bythe receiver may be calibrated to the selected harmonic of thefundamental transmission frequency, particularly to the second harmonic.

[0079] For instance, when considering a basic frequency of 2 MHz, andtypical resistance and capacitance values for the assembly composed ofthe probe 6 and the cable 206 of Cp=400 pF (whereof 300 pF due to theceramic material and 100 pF to the cable); Rp=400 O, it is apparent thata compensating inductance Lc of 15 μH causes the transmit circuit toresound at the frequency of 2 MHz.

[0080] When further considering typical values of parasitic capacitanceand resistance for the receivers 5, such as Rr=4 kO; and Cr=100 pF, theresonance frequency of the circuit, in combination with saidcompensating inductance Lc of 15 μH results to be 4 MHz, i.e. at thesecond harmonic of the fundamental frequency of the transmitted pulse.

[0081] If the parasitic capacitance Cr is not such as to allow propertuning to the second harmonic upon reception, a compensating capacitorCc may be placed in parallel to Cr, so that Cc+Cr are approximatelyequal to Cp/4. This allows to maintain the tuning inductance on anoptimized value for transmission and to also tune the transmittingresonant circuit.

[0082] It is important to notice that the above concepts may be alsoinverted, i.e. the tuning inductance may be set on the receiver, and acompensating capacitor may be considered which, in combination with saidtuning inductance, optimizes tuning of the transmitting resonantcircuit.

[0083] As mentioned above, the optimized tuning inductance may bedirectly mounted on the probe-cable assembly, regardless of the specificultrasound imaging machine, as the transmitting resonant circuit istuned regardless of the characteristics of the transmitter 3.

[0084] Here, each probe-connecting cable assembly would have its owntuning inductance which is determined based on the electriccharacteristics of said specific assembly.

[0085] Regarding the presence of the compensating capacitor, the lattermight be set after selecting a predetermined assembly, if the tuningcapacitor provided with the probe and the cable could not allowoptimized tuning of the receiving resonant circuit.

[0086] Advantageously, according to a first improvement, the probe 6might include a memory 306 for storing the relevant electric data fortuning the receiving resonant circuit, and particularly the value of thecompensating inductance associated to the probe and the value of theequivalent capacitor of the probe-cable assembly. When the probe andcable are connected to the ultrasound imaging machine, the centralprocessing unit 1 might read data from the memory 306 of the probe 6.Based on said data, the processing unit 1 may first determine if acompensating capacitor is to be set for the receiving channel. When acompensating capacitor is needed, said processing unit may secondlydetermine the value of said compensating capacitor and set a variablecapacitor provided in the receiving channel parallel to the parasiticcapacitance of the receiver 5 to said capacitance value.

[0087] However, in accordance with another alternative characteristic,the memory 306 of the probe may only contain one identification code,whereas the memory 8 may contain several tables of data relating toseveral different probe-cable assemblies, as well as a software programfor reading the identification code stored 306 in the probe 6 and forcomparing it with the list of identification codes included in thememory 8 and uniquely associated to tables of electric data of theassembly identified by said code whereby, once the data table whose codecoincides with the one read from the memory 306 of the probe is found,the procedure of setting the compensating capacitor of the receivingresonant circuit is executed as described above.

[0088] If no table is found to correspond to the identification codeprovided by the probe, the comparing program directly requests datathrough a message, e.g. displayed on the screen 9 or transmitted by anyother means, possibly sound. In this case, a portable magnetic mediummay be provided in combination with the probe, with the correspondingdata table stored therein, which may be read 10 by the machine by meansof a special reader 10, whereby the data may be loaded into the memory 8and the set up procedure may be executed as described above. The aboveprocedures may be executed in a manner similar to the installation ofdrivers for computer devices or the like, like plug and play procedures.

[0089] As is apparent from FIG. 1, the set up procedure as describedabove for the compensating capacitor of the resonant circuit in thereceiving channel is also applicable to the resonant circuit tuninginductance in the transmission channel.

[0090] In this case, the inductance might not be placed on theprobe-cable assembly, but at the input of the ultrasound imagingmachine. By using a variable inductance, controlled by the centralprocessor 10 on the basis of the electric data of the probe-cableassembly, the ultrasound imaging machine may be arranged toautomatically or semiautomatically set said tuning inductance to anoptimized value for the probe-cable assembly being used. It shall benoted that, here again, all the above considered options for setting thecompensating capacitor to tune the resonant circuit in the receivingchannel may be provided. It shall be further noted that, in the samemanner as the compensating capacitor may be set to zero, i.e. excludedfrom the circuit, even the variable tuning inductance provided insidethe ultrasound imaging machine may be reduced to zero or by-passed, ifthe probe already has a tuning inductance integrated thereon, as thiswould result from the information provided either automatically by thememory integrated in the probe or by the tables contained in the memoryof the ultrasound imaging machine, or by the data contained in anyportable storage media.

[0091] The above description clearly shows the advantages of theinvention. First, the invention allows to remove or reduce the spurioussignal components upon transmission. Moreover, the resonant circuit maybe tuned directly on the probe, regardless of the ultrasound imagingmachine in use. The provision of a tuning inductance also has an effecton the receiving channel, which is also similar to a resonant circuit,to be tuned in most cases to the second harmonic resonance frequencyalready based on the tuning inductance for the transmitting resonantcircuit.

[0092] The transmitting and/or receiving resonant circuits may be tunedin several possibly automatic or semiautomatic manners. Particularly, bycoupling the receiving channel to the probe through a resonant circuitwhich is tuned or may be tuned to the second harmonic frequency, anycontribution to the received signal due to the second harmonic may beseparated from those at the fundamental frequency, without using thecomplex filtering procedures currently required, or anyway limiting theuse of said procedures.

[0093] Obviously, the method and apparatus of this invention find use inany ultrasound imaging mode, particularly in any ultrasound imaging modeusing contrast agents and/or received signals at a harmonic of thefundamental frequency of the transmitted pulses.

[0094] The method according to the present invention may be combinedwith any other kind of ultrasound imaging method for example with amultiple pulse technique employing modulated wavelets which providecoding upon transmission and correlated filtering upon reception,wherein the term wavelets includes arbitrary analog signals not havingdiscrete times and amplitudes as well as pulse sequences having discretetimes and amplitudes.

[0095] Alternatively the method according to the invention may becombined with a so called Pulse Inversion technique, in which only a fewcomponents of the at least two successive transmitted pulses areinverted, whereas the other components are not inverted, the receivedsignals being summed together as described in U.S. Pat. No. 5,706,819(issued Jan. 13, 1998 to Hwang et al.) which patent is expresslyincorporated by reference herein.

[0096] A further improvement may provide the method according to thepresent invention in combination with a multi pulse technique, in whichan even number of pulses half of which is inverted with respect of theother half number of the said pulses are transmitted and the receivedsignals relating to all or al least part of these transmitted pulses issummed together. In this case for example for each scan line four pulsesare transmitted, two of which are inverted with respect of the othertwo, the order of transmission of the said four pulses being of anykind, particularly the normal and inverted pulses are transmittedalternatively one to the other or the two inverted pulses aretransmitted directly one after the other as the first two, the last twoor the intermediate two pulses.

[0097] According to yet another variant the method according to thepresent invention may be combined with an imaging technique providingthe emission of two successive transmission pulses and the reception ofthe two reflection echo signals generated by said transmission pulsesand in which means are provided for differentiating the two reflectedecho signals from each other.

What is claimed is:
 1. A method for transmitting ultrasound pulses andreceiving echo signals at a harmonic of the transmission frequencyincluding the steps of generating a signal for exciting a transducer totransmit at least one ultrasound pulse at a basic transmission frequencyand the steps of receiving the reflection echo of said pulse at aharmonic of the frequency of the transmitted pulse, any contributions tothe harmonic frequency being removed or attenuated in the signal forexciting pulse transmission, characterized in that the signal forexciting the transducer/s is filtered or coupled thereto via a resonantcircuit which is calibrated to the basic frequency.
 2. A method asclaimed in claim 1, characterized in that, alternatively thereto or incombination therewith the invention provides that the transducer/s arefiltered or coupled to a receiver through a resonant circuit which iscalibrated to the receive harmonic frequency, particularly to the secondharmonic of the basic frequency of the transmitted pulse.
 3. A method asclaimed in claim 1 or 2, characterized in that the assembly composed ofthe transducer/s and the cable connecting it to a transmitter whichgenerates electric pulses for exciting the transducer/s is used as atransmitting resonant circuit, the resonance frequency being adjusted tothe basic frequency by inserting an inductance in series between theconnecting cable and the transmitter.
 4. A method as claimed in one ormore of the preceding claims, characterized in that the receivingresonant circuit consists of the receiver itself which, upon reception,operates like a resonant circuit having predetermined resistance andcapacitance values.
 5. A method as claimed in one or more of thepreceding claims, characterized in that a tuning inductance is providedfor tuning the receiving resonant circuit.
 6. A method as claimed in oneor more of the preceding claims, characterized in that the receivingresonant circuit tuning inductance is set in such a manner that theresonance frequency is a harmonic, particularly the second harmonic ofthe transmission frequency.
 7. A method as claimed in one or more of thepreceding claims, characterized in that the receiving resonant circuittuning inductance is set in such a manner that the resonance frequencyis the same tuning inductance as provided for the transmitting resonantcircuit and has the same value.
 8. A method as claimed in claim 7,characterized in that a compensating capacitor is provided, which may beconnected in parallel with the parasitic capacitance of the receiver totune the receiving resonant circuit in combination with a tuninginductance in common with the transmitting resonant circuit or havingthe same value as the latter.
 9. A method as claimed in one or more ofthe preceding claims, characterized in that the compensating capacitancesubstantially corresponds to a quarter of the capacitance of theassembly composed of the transducer/s and the connecting cable.
 10. Amethod as claimed in one or more of the preceding claims, characterizedin that it provides a variable capacitor, controlled by a control unitand means for reading relevant electric data of the assembly composed ofthe transducer/s and the connecting cable.
 11. A method as claimed inone or more of the preceding claims, characterized in that a variabletuning inductance is provided, controlled by a control unit and meansfor reading relevant electric data of the assembly composed of thetransducer/s and the connecting cable.
 12. A method as claimed in claim10, characterized in that it provides that a memory is associated to theassembly composed of the transducer/s and the connecting cable, whichmemory contains the relevant electric data for the resonant circuitformed by said assembly and may be read by the control unit to set saidvariable capacitor to the proper capacitance value with reference to thedata of the assembly composed of the transducer/s and the connectingcable.
 13. A method as claimed in claims 10 to 12, characterized in thatit provides that a memory is associated to the assembly composed of thetransducer/s and the connecting cable, which memory contains therelevant electric data for the resonant circuit formed by said assemblyand may be read by the control unit to set said variable inductance tothe proper inductance value with reference to the data of the assemblycomposed of the transducer/s and the connecting cable.
 14. A method asclaimed in one or more of claims 10 to 13, characterized in that itprovides a memory associated to the unit for controlling the variablecapacitor and/or the variable inductance, said memory containing thedata of several different transducer/s-connecting cable assemblies, andeach of said assemblies being uniquely identified by an identificationcode, whereas said code may be manually set or read by the control unitfrom a memory associated to each transducer/s-connecting cable assembly.15. A method as claimed in one or more of claims 10 to 14, characterizedin that a memory is associated to the control unit for setting up thevariable capacitor and/or the variable tuning inductance, in whichmemory a software program is loaded which detects the presence of a datatable with the reference code of a specific transducer/s-cable assembly,as well as a program which automatically requests said data either bymanual setting or by automatic reading of a portable storage medium whenno data relating to the transducer/s-cable assembly is detected.
 16. Amethod as claimed in one or more of the preceding claims, characterizedin that the tuning inductance is associated to the transducer/s-cableassembly and/or to the transmitter and to the receiver, and that in thelatter case it is of the variable type.
 17. A method as claimed in oneor more of the preceding claims, characterized in that thetransducer/s-cable assembly consists of an ultrasound imaging probe withthe corresponding connecting cable.
 18. A method as claimed in one ormore of the preceding claims, characterized in that the transmitter andthe receiver are parts of the transmission and reception chain of anultrasound imaging machine.
 19. A method for transmitting ultrasoundpulses and receiving echo signals at a harmonic of the transmissionfrequency including the steps of generating a signal for exciting atransducer to transmit at least two successive ultrasound pulses at abasic transmission frequency, which at least two successive pulses areidentical or one of the at least two pulses is inverted relative to theother or is 180° dephased, and which at least two transmitted pulses arefocused along the same scan line, and the steps of receiving thereflection echoes of said at least two successive transmitted pulses toextract the echo component at a harmonic or sub-harmonic of thefrequency of the transmitted pulses, particularly a second harmonic ofthe fundamental frequency of the transmitted pulses, characterized inthat the frequency of the received echoes is filtered by means of aresonant circuit which allows the transducer to be coupled to areceiver, which resonant circuit is tuned to the selected harmonic orsub-harmonic frequency, particularly to the second harmonic of thefundamental frequency of the transmitted pulses.
 20. A method as claimedin claim 19, characterized in that any contributions to the harmonic orsub-harmonic frequency is removed or attenuated in the signals forexciting pulse transmission, by coupling the transducers with a resonantcircuit which is calibrated to the basic frequency.
 21. A method asclaimed in claim 19 or 20, characterized in that it has thecharacteristics as claimed in one or more of the preceding claims 1 to18.
 22. A method as claimed in one or more of claims 1 to 21,characterized in that it provides the combination with a Pulse Inversionimaging technique or the like, in which image reconstruction data isobtained by the difference or the sum of the reflection echoes of atleast two successive transmitted pulses focused along the same line ofview, which are identical or inverted or 1800 dephased relative to eachother.
 23. An apparatus for transmitting ultrasound pulses and receivingecho signals at a harmonic of the transmission frequency, for example toan ultrasound imaging machine comprising: a transmitter (3) whichgenerates electric signals for exciting at least one transducer totransmit ultrasound pulses at a predetermined basic frequency, areceiver (5) whereto electric signals are provided from one or moretransducers which pick up reflected echo signals at a harmonicfrequency, particularly a second harmonic of the frequency of thetransmitted pulses and means (6, 206, 5, 12, 13) for removing ordrastically attenuating the contributions of harmonic components,particularly those at the second harmonic in transmitted pulses, saidmeans consisting of a resonant circuit (6, 206) which allows to couplethe transducer/s to the transmitter (6, 106), whose resonance frequencyis set to the basic frequency of the transmitted pulses.
 24. Anapparatus as claimed in claim 13, characterized in that the resonantcircuit consists of the assembly composed of the transducer/s (6, 106)and the connecting cable (206), there being provided an inductance (12)for tuning the resonance frequency of said resonant circuit to the basicfrequency of the transmitted pulses.
 25. An apparatus as claimed inclaim 24, characterized in that the tuning inductance (13) is connectedin series to the resistor of the assembly composed of the transducer/s(6, 106) and the output of the transmitter (3).
 26. An apparatus asclaimed in claim 24 or 25, characterized in that the transmitter (3) isa low impedance generator.
 27. An apparatus for transmitting ultrasoundpulses and receiving echo signals at a harmonic of the transmissionfrequency, for example to an ultrasound imaging machine comprising: atransmitter which generates electric signals for exciting at least onetransducer to transmit ultrasound pulses at a predetermined basicfrequency, a receiver whereto electric signals are provided from one ormore transducers which pick up reflected echo signals at a harmonicfrequency, particularly a second harmonic of the frequency of thetransmitted pulses and means for removing or drastically attenuating thecontributions of components which do not correspond to a specificharmonic, particularly to the second harmonic of the frequency oftransmitted pulses, said means consisting of a resonant circuit whichallows to couple the transducer/s (6, 106) to the receiver (5), whoseresonance frequency is set to a predetermined harmonic frequency,particularly to the second harmonic of the fundamental frequency of thetransmitted pulses.
 28. An apparatus as claimed in claim 27,characterized in that the resonant circuit consists of the receiver (5),i.e. of the resistor and the parasitic capacitance thereof.
 29. Anapparatus as claimed in claim 27 or 28, characterized in that itincludes the characteristics as claimed in one or more of the precedingclaims 23 to
 26. 30. An apparatus as claimed in one or more of claims 23to 29, characterized in that the assembly composed of the transducer/s(6, 106) and the connecting cable (206) is alternatively connected tothe transmitted (3) and to the receiver (5) through switching means (7).31. An apparatus as claimed in one or more of the preceding claims 23 to30, characterized in that the tuning inductance (12) for thetransmitting resonant circuit and for the receiving resonant circuithave identical values.
 32. An apparatus as claimed in claim 31,characterized in that a common tuning inductance (12) is provided forthe transmitting resonant circuit and for the receiving resonantcircuit.
 33. An apparatus as claimed in one or more of the precedingclaims, characterized in that, in combination with the tuning inductance(12), a compensating capacitor is associated to the receiving resonantcircuit, to allow tuning to the proper resonance frequency.
 34. Anapparatus as claimed in claim 33, characterized in that the compensatingcapacitor (13) is connected in parallel with the parasitic capacitanceof the receiver (5).
 35. An apparatus as claimed in claim 33 or 34,characterized in that the compensating capacitor is selected in such amanner that the sum of the parasitic capacitance and the compensatingcapacitance corresponds to a quarter of the capacitance of thetransmitting resonant circuit, i.e. of the capacitance of the assemblycomposed of the transducer/s (6, 106) and the connecting cable (206).36. An apparatus as claimed in one or more of the preceding claims 33 to35, characterized in that the compensating capacitor is a variablecapacitor.
 37. An apparatus as claimed in one or more of the precedingclaims 23 to 36, characterized in that it includes means forautomatically setting up the variable compensating capacitor (13); therebeing provided a control unit (1) and a memory (306, 8) associated tothe assembly composed of the transducer/s (6, 106) and the connectingcable (206), which memory contains the data relating to the electriccharacteristics of the resonant circuit formed by said assembly and ofthe tuning inductance (12), said memory (306, 8) being read by thecontrol unit, and said control unit including a software program fordetermining the value of the compensating capacitor (13) and for settingthe variable compensating capacitor (13) to said value.
 38. An apparatusas claimed in one or more of the preceding claims, characterized in thatthe memory (396) is associated to the assembly composed of thetransducer/s (6, 106) and the connecting cable (206).
 39. An apparatusas claimed in one or more of the preceding claims, characterized in thatthe memory (8) is. associated to the receiver (5) and/or to the controlunit (1).
 40. An apparatus as claimed in one or more of the precedingclaims 37 to 39, characterized in that the memory (306) associated tothe assembly composed of the transducer/s (6, 106) and the connectingcable (206) contains one code for uniquely identifying said assembly,whereas the memory (8) associated to the receiver (5) and/or to thecontrol unit (1) contains a plurality of data tables, each relating to aspecific assembly composed of the transducer/s (6, 106) and theconnecting cable (206) and each related to the unique identificationcode of said specific assembly, there being provided a software programfor reading the code stored in the memory (306) of the assembly composedof the transducer/s (6, 106) and the connecting cable (206) and forsearching a data table identified by said code in the memory (8)associated to the receiver (5) and/or to the control unit, and a programfor reading said table and for setting up the compensating capacitor(13) based on the data contained therein.
 41. An apparatus as claimed inone or more of the preceding claims 37 to 40, characterized in thatmeans (10) for reading a portable storage medium are associated to thecontrol unit (1), whereas a portable storage medium is associated to theassembly composed of the transducer/s (6, 106) and the connecting cable(206), which storage medium contains the data relating to said assembly,the memory (8) associated to the control unit (1) containing a programwhich prompts to insert said portable storage medium in the reader (10)when no data table corresponding to the identification code of theassembly composed of the transducer/s (6, 106) and the connecting cable(206) has been found, and which reads data from said portable storagemedium, transfers it into the memory (8) and executes the program fordetermining and setting the capacitance of the variable capacitor (13).42. An apparatus as claimed in one or more of the preceding claims 37 to41, characterized in that it has sensors for connecting the assemblycomposed of the transducer/s (6, 106) and the connecting cable (206) toa connection port, said sensors being connected to the control unit (1)which automatically executes the programs for reading the memories (306,8) or the portable storage medium and the programs for determining andsetting the capacitance of the compensating capacitor (13)
 43. Anapparatus as claimed in one or more of the preceding claims,characterized in that the tuning inductance (12) for the transmittingresonant circuit is permanently associated to the assembly composed ofthe transducer/s (6, 106) and the connecting cable (206).
 44. Anapparatus as claimed in one or more of the preceding claims 37 to 42,characterized in that the tuning inductance (12) is permanentlyassociated to the transmitter (3) and is a variable inductance, and thatit can be set to certain values by the control unit (1) which executesprograms for reading the electric data of the assembly composed of thetransducer/s (6, 106) and the connecting cable (206), which data isstored in a memory (306) integrated in said assembly and/or in thememory (8) and/or on portable storage media, which programs are like theprograms for setting the capacitance of the variable compensatingcapacitor (13) as claimed in claims 37 to 42 and are loaded in thememory (8) associated to said control unit (1).
 45. An apparatus asclaimed in one or more of the preceding claims 23 to 43, characterizedin that the assembly composed of the transducer/s (6, 106) and theconnecting cable (206) consists of an ultrasound imaging probe.
 46. Anapparatus as claimed in one or more of the preceding claims,characterized in that the transmitter (3), the receiver (5), the switch(7), the compensating capacitor (13) and/or the variable inductance(12), the control unit (1), the memory (8) and possibly the unit (10)for reading portable storage media are parts of an ultrasound imagingmachine.
 47. An apparatus for transmitting ultrasound pulses andreceiving echo signals as claimed herein, for instance an ultrasoundimaging machine including a transmitter which generates electric signalsfor exciting at least one transducer to transmit ultrasound pulses at apredetermined basic frequency, a receiver whereto electric signals areprovided from one or more transducers which pick up reflected echosignals at a harmonic or sub-harmonic frequency, particularly a secondharmonic of the frequency of the transmitted pulses and a resonantcircuit through which the transducer/s are coupled to the receiver,whose resonance frequency is set to a harmonic or sub-harmonic frequencyof the basic frequency of the transmitted pulses, particularly to asecond harmonic of the frequency of the transmitted pulses, there beingprovided means for transmitting, for each line of view, at least twosuccessive identical or phase-inverted transmission pulses and means forcombining the received reflection echoes, caused by said two pulses inthe form of a subtraction or a sum of the two reflection echoesrespectively, such as a summer or subtracting circuit.
 48. An apparatusas claimed in claim 47, characterized in that the transducer/s, i.e. theprobe is also coupled to the transmitter through a resonant circuitcalibrated to the fundamental frequency of the transmitted pulses. 49.An apparatus as claimed in claim 47 or 48, characterized in that it hasthe characteristics as claimed in one or more of the preceding claims 23to
 46. 50. An ultrasound imaging probe comprising at least onetransducer or a plurality of transducers (106) and a cable (206) forconnection to a port of an ultrasound imaging machine, characterized inthat it integrates an inductance for tuning the equivalent resonantcircuit formed by said probe (6).
 51. An ultrasound imaging probecomprising at least one transducer or a plurality of transducers (106)and a cable (206) for connection to a port of an ultrasound imagingmachine, characterized in that it integrates a memory (306) which may beaccessed through the connecting cable (206) and stores all data relatingto the electric characteristics of the equivalent resonant circuitand/or an unique identification code.
 52. An ultrasound imaging probe asclaimed in claim 51, characterized in that it has the characteristics asclaimed in claim 51, with the memory (306) containing the data relatingto the tuning inductance.
 53. An ultrasound imaging machinecharacterized in that it is provided in combination with an ultrasoundimaging probe (6) and that the probe (6) and the machine include thecharacteristics as claimed in one or more of claims 23 to
 52. 54. Amethod as claimed in one or more of the preceding claims 1 to 22,characterized in that it is provided in combination with a multiplepulse technique employing modulated wavelets which provide coding upontransmission and correlated filtering upon reception, wherein the termwavelets includes arbitrary analog signals not having discrete times andamplitudes as well as pulse sequences having discrete times andamplitudes
 55. A method as claimed in one or more of the precedingclaims 1 to 22 or 54, characterized in that it is combined with a PulseInversion technique, in which only a few components of the at least twosuccessive transmitted pulses are inverted, whereas the other componentsare not inverted, the received signals being summed together.
 57. Amethod according to one or more of the preceding claims 1 to 22 or 54,Or 55, characterized in that it is combined with a multi pulsetechnique, in which an even number of pulses half of which is invertedwith respect of the other half number of the said pulses are transmittedand the received signals relating to all or al least part of thesetransmitted pulses is summed together.
 58. A method according to claim57, characterized in that four pulses are transmitted two of which areinverted with respect of the other two, the order of transmission of thesaid four pulses being of any kind, particularly the normal and invertedpulses are transmitted alternatively one to the other or the twoinverted pulses are transmitted directly one after the other as thefirst two, the last two or the intermediate two pulses.
 59. A method asclaimed in one or more of the preceding claims 1 to 22 or 54 to 58,characterized in that it is combined with the emission of two successivetransmission pulses and with the reception of the two reflection echosignals generated by said transmission pulses and with means fordifferentiating the two reflection echo signals from each other.